The field of the disclosure relates generally to temperature monitoring, and more specifically, to methods and systems for electrically-based, passive, wireless temperature monitoring.
Pilots and maintenance personnel have a need to monitor a spatial distribution of temperature over the volume surrounding the engine core of a jet engine, for example. The operating temperatures in the engine core surrounding volume may range from about 100 degrees Fahrenheit to about 2000 degrees Fahrenheit. An ability to provide such a monitoring capability would lead to improved maintenance efficiency and provide an advance warning of potential engine malfunctions.
Current engine fire and overheat detection temperature sensors consist of long loops that respond to temperature changes with changes in pneumatic pressure, net loop resistance or net loop dielectric value. Systems of this type provide average dimensionless temperature “event” numbers. As such these systems do not provide a desired spatial resolution. These sensor systems also incorporate direct electrical connections. This is important since a substantial percentage of the weight of these current systems comes from the brackets and support structure needed for the electrical interconnections, so that the sensors loops survive the harsh vibrations encountered in such environments.
Electronic temperature sensors generally include, electromechanical devices (like traditional bimetal thermostats and the pneumatic tubes described above) which employ differential expansion of dissimilar metals or other materials usually activating a switch, and thermocouples which generate a voltage across an electrical contact between dissimilar metals proportional to temperature and the electronic work functions of the metals. Also included are thermistors which contain materials that have a large change in overall bulk electrical resistance with temperature. Band-gap type electronic thermometers which rely on voltage differences between semiconductor junctions operating at different current densities are also known.
In general, no semiconductor based electronic devices are available in a material system that will continue to operate up to the 2000 degree Fahrenheit temperature range mentioned above. For example, wide band gap materials like silicon carbide operate only up to around 1100 degrees Fahrenheit. Vacuum tube type electronics might be designed to operate up to 2000 degrees Fahrenheit, however such technology is not practical for low power miniaturized systems. Therefore the above described electromechanical and thermistor sensors are currently used in jet engine temperature monitoring.
Continuing, the electromechanical and thermistor engine temperature sensors in use today do not provide information on the spatial dependence of the temperature and therefore cannot be used to conclusively locate possible hot spots on the engine. Existing solutions also require wired connections to the sensors. Thermocouple, thermistor, and electromechanical type sensors cannot in general cover wide areas while also providing accurate measurement of localized hot spots. To address such issues, a large number of individual thermocouples, thermistors, or electromechanical sensors might be used. However such a solution would require a large number of wires or a mechanical switching network since an electronic multiplexing switch would not operate over the required temperature range. The end result is that such a system would be unacceptably heavy and complex.
Further, solid state infra-red imaging cameras cannot operate at the required temperatures, and moving them far enough away is also not mechanically practical. Vacuum tube cameras and supporting electronics are also not practical. A large number of cameras or observation points would be required to cover the entire engine surface. It might be possible to develop an optical or fiber-optical system to achieve coverage of the entire engine surface, but these would also not be practical or cost effective within the limited space.